When Congress spends more money than it collects in taxes, it authorizes the Treasury Department to borrow from the public by selling Treasury bills, bonds, and notes. The Treasury offers these securities for sale at public auction, and they are bid for and purchased by banks, pension funds, trusts, corporations, individuals, and even foreign interests. These are widely considered to be the safest IOUs around. After all, they are guaranteed by the U.S. government. Inasmuch as Treasury securities are offered at auction, there is no chance they will not be purchased. The Treasury can offer as high a rate of...